In Beadle and Tatum’s study of Neurospora , they were able to identify three classes of arginine auxotrophs, mutants that needed arginine added to minimal media in order to grow. The pathway in the production of arginine includes the following steps: precursor ornithine citrulline arginine. What nutrient(s) had to be added to the minimal medium in order for the class of mutant with a defective enzyme for the precursor ornithine step to grow?

citrulline only
precursor only
precursor, ornithine, and citrulline
ornithine or citrulline